Scanning electrochemical microscopy (SECM) is a powerful scanning probe microscopy (SPM) imaging method used for evaluating the chemical and physical properties of materials at microscopic and nanoscopic length scales. The vast majority of SECM measurements performed to date have used conventional ultramicroelectrode (UME) probes, which typically consist of a metallic wire sealed in an insulating glass sheath. During operation, the electrochemical interaction between this UME “point probe” and the sample are recorded in a point-by-point sensing scheme as the UME is scanned across an area of interest. A major shortcoming of conventional point probes is that they require very long scan times to image large sample areas with high resolution. In general, long scan times result in low throughput and can lead to unwanted changes in the sample or probe.
Previous research efforts have attempted to overcome the trade-off between resolution and areal imaging rates through a variety of approaches that have involved modifications to SECM hardware, the use of advanced probe geometries, and/or post measurement image processing to correct for blurriness and artifacts associated with fast scan speeds. For example, the development of scanning droplet cells for scanning electrochemical cell microscopy (SECCM), combined with the use of more efficient spiral scan patterns, has resulted in substantial increases in areal imaging rates thanks to their ability to utilize high scan rates without being limited by convection. Alongside instrument development, the use of innovative probe configurations and geometries has emerged as a promising approach to increase SECM imaging rates. For example, multiple studies have demonstrated the use of individually addressable sub micrometer electrodes for large area imaging. Other previous research combined the idea of using a linear array of microelectrodes with polymeric thin films to create soft, flexible probes capable of imaging large sample areas, even for tilted and curved surfaces. Yet, the resolution of these probes remains limited by the lateral spacing between the point probes embedded within the array. Additionally, fabrication of these probes is nontrivial, and more complex electronics (e.g. multiplexer or multichannel potentiostat) are required to analyze the signals from the individually addressable electroactive elements.
In chemical microscopy, various image post-processing strategies have been introduced for producing high-quality images from undersampled datasets. Understanding the number of measurements to reconstruct a continuous signal is also a concern in signal processing. For example, the classical Shannon-Nyquist theorem dictates the resolution of point sampling required to accurately construct a bandlimited image. While this result plays a role in areas ranging from RF communications to audio processing, for imaging it may be suboptimal: real images are not just bandlimited—they may possess additional structure, which, if used appropriately, can reduce the number of measurements required for accurate imaging. For example, in chemical microscopy, a sample of interest may include relatively sparse electrocatalytic features. The number of such features is one measure of the “information content” of the image, and is typically much smaller than the number of image pixels.